Orforglipron (Foundayo) vs Tirzepatide (Mounjaro): Comparison

Tirzepatide, sold under the brand name Mounjaro, is currently the most effective approved weight loss medication in the UK. But the landscape is changing fast, with new oral GLP-1 weight loss pills offering similar benefits without injections.

One of them is orforglipron, sold under the brand name Foundayo, a once-daily pill that was approved in the US in April 2026. It isn't yet available in the UK, but approval is expected by late 2026. So, which works better for weight loss? Here's what the evidence shows.

Key Takeaways

• Orforglipron is a once-daily GLP-1 pill, approved in the US in April 2026 under the brand name Foundayo
• Tirzepatide (Mounjaro) is a weekly injection targeting both GLP-1 and GIP
• Over 72 weeks, tirzepatide achieved up to 22.5% weight loss vs 11.1% for orforglipron at the highest approved dose
• Both have similar digestive side effects like nausea and diarrhoea, which usually ease over time
• Tirzepatide is available now in the UK; orforglipron is expected by late 2026

Orforglipron vs tirzepatide: What’s the difference?

What is orforglipron (Foundayo)?

Orforglipron, sold as Foundayo in the US, is a once-daily weight loss pill. It belongs to a family of medicines called GLP-1 receptor agonists, which includes injections like Wegovy and Saxenda, and the oral Wegovy pill. Unlike other oral GLP-1 medications, Foundayo can be taken at any time of day, with or without food.

What is tirzepatide (Mounjaro)?

Tirzepatide is the active ingredient in Mounjaro, a weekly weight loss injection approved in the UK. It's currently the most effective approved weight loss medicine available. Tirzepatide works on two natural hormones (GLP-1 and GIP) rather than one, which contributes to its strong results.

Do orforglipron and tirzepatide work differently?

Yes. Orforglipron works by mimicking the effects of GLP-1, a natural hunger hormone. This curbs your appetite and makes you feel full, so you eat less.

Mounjaro does that too. It also activates another hormone, GIP, which enhances insulin release and may further support weight loss. This dual action contributes to Mounjaro's greater effectiveness in trials.

Orforglipron vs tirzepatide: weight loss results

Two key trials show the difference:

• In the ATTAIN-1 trial, people taking the highest approved 17.2mg dose of orforglipron lost an average of 11.1% of their body weight over 72 weeks.
• In the SURMOUNT-1 trial, people on the highest 15mg dose of Mounjaro lost up to 22.5% of their body weight over 72 weeks.

Tirzepatide produces greater weight loss at its highest dose, but orforglipron's results are still significant for a daily tablet.

Does orforglipron cause more side effects than Mounjaro?

There's no trial that has directly compared the two, but here's what we know from their separate clinical trials.

Both medications share the same most common side effects: digestive issues like nausea, vomiting, constipation, and diarrhoea, which are usually mild to moderate.

The main difference is how many people stop treatment because of side effects:

• In the ACHIEVE-4 trial, around 10.6% of people stopped taking orforglipron at the highest 17.2mg dose because of orforglipron side effects.
• In the SURMOUNT-1 and SURMOUNT-2 trials, around 4.3% of people stopped taking Mounjaro at the highest 15mg dose because of Mounjaro side effects.

Side effects support at Voy

"If you're using Voy and you experience any side effects, rest assured that our expert clinicians are just a message or phone call away. They can adjust your dose, prescribe medication to ease your symptoms, or simply offer reassurance.

Everyone responds differently to weight loss treatment and we'll help you find what feels right for you."

Phoebe Fox - Weight Loss Specialist

Orforglipron vs Mounjaro: dosing schedule

Both medications use a step-by-step dose escalation, starting at the lowest dose and increasing gradually if tolerated well. This helps the body adjust and reduces side effects.

Here's how the dosing schedules compare:

• Orforglipron (Foundayo) is a once-daily tablet with six dose levels: 0.8mg, 2.5mg, 5.5mg, 9mg, 14.5mg, and 17.2mg. Dose increases happen every 30 days, if tolerated.
• Mounjaro is a once-weekly injection with six dose levels: 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg, and 15mg. Dose increases happen every four weeks, if tolerated.

Foundayo can be taken at any time of day, with or without food. The tablet should be swallowed whole, not broken, crushed, or chewed. Mounjaro can also be injected at any time of day, on the same day each week.

Although Foundayo is a daily tablet, some people may prefer it to a weekly injection.

Can you switch from Mounjaro to orforglipron?

Not yet, because orforglipron isn't currently approved in the UK. But the ATTAIN-MAINTAIN trial has tested whether orforglipron could work as a maintenance treatment after losing weight on an injection.

In the trial, people who had already lost weight on Zepbound (the US version of Mounjaro for weight loss) or Wegovy were given either orforglipron or a placebo. After 24 weeks:

• People switching from Wegovy to orforglipron stayed at almost the same weight (0.1kg change), while those on placebo regained 9.4kg.
• People switching from Zepbound to orforglipron regained 2.6kg, while those on placebo regained 9.1kg.

This suggests orforglipron could work as a maintenance option once weight loss is achieved on injections like Mounjaro, helping prevent the significant weight regain that often happens when treatment stops.

UK switching protocols haven't been confirmed and will depend on when orforglipron is approved.

Orforglipron vs Mounjaro: cost and UK availability

Mounjaro is the available option in the UK right now. You can get it on the NHS if you meet certain criteria, or via private prescription for £150 to £350 per month, depending on the provider.

Orforglipron isn't approved in the UK yet, so UK pricing hasn't been set. In the US, Foundayo costs $25 a month with commercial insurance, or $149 a month for self-pay.

Based on how Wegovy and Mounjaro rolled out, orforglipron is most likely to reach UK patients privately first. If it eventually makes it to the NHS, you'd pay the standard prescription charge (currently £9.90 per item in England, with prescriptions free in Scotland, Wales, and Northern Ireland).

Which is better: orforglipron or Mounjaro?

Mounjaro is more effective for weight loss based on trial data. People on the highest 15mg dose of Mounjaro lost up to 22.5% of their body weight over 72 weeks, compared to 11.1% for orforglipron at the highest US-licensed 17.2mg dose.

But the right choice depends on your circumstances:

• Mounjaro may suit you better if: you want the strongest weight loss results and don't mind weekly injections. It's the stronger option for people actively trying to lose weight.
• Orforglipron may suit you better if: you'd prefer a daily tablet, want to avoid injections, or are looking for a maintenance option after losing weight on an injection.

Once orforglipron (Foundayo) becomes available in the UK, our clinical team will support you in deciding what's right for you. At Voy, we currently offer Wegovy, Mounjaro, and Orlos (orlistat) weight loss tablets. Take our quiz to see which option might work for you.